1. Field Of The Invention
The present invention relates to a method and a device for navigating, by indirect vision, in a surrounding world which is captured by one or more image sensors and displayed to a user via a display device which in use is in front of the user's head and follows the movements of his head. The display device can be headworn or handheld or arranged on a mechanical device so that it can be positioned in front of the user. The latter can occur, for instance, by the display device being carried by an arm so that it can be moved with the user's hand or in some other manner in front of the user when swivelling on a chair capable of rotating. In the following only the headworn case will be discussed since as a rule this is most relevant, but there may be situations when the display device is held in front of the user's eyes in some other way, but otherwise functions just like in the headworn case.
2. Description Of The Related Art
In military contexts it is important to have a visual perception of the surrounding world. The surrounding world is usually registered directly by the eyes or via an optical periscope. Such periscopes can be found, for example, in combat vehicles or in submarines. However, new requirements and threats have created a need to be able to obtain a perception of the surrounding world via image sensors, usually cameras, whose image data is displayed, for instance, on a screen. This technique is referred to as indirect vision. In these contexts image data is captured and displayed in real time, which here means at such a speed that the user experiences a continuity in movements. A number of 20 images per second is usually considered a minimum for real time, but may in some cases be lower.
Indirect vision is used for several reasons. One reason is to be able to capture image information that the eye cannot see. By using, for example, image sensors of the Night Vision type or image sensors sensitive to thermal IR radiation, the perception of the surrounding world can be reinforced. Another reason for indirect vision is to protect the eyes against eye-damaging laser radiation. In military context, a combat vehicle may also reveal itself by the light or radiation emitted from the illuminated interior via an optical periscope.
The images that are displayed by indirect vision to a user may come from an image sensor device in real time or recorded, from a virtual surrounding world or as a combination of these techniques. An image sensor device may comprise, for instance, one or more video cameras sensitive to the visual wavelength band, IR cameras sensitive in one of the IR bands (near IR, 3-5 μm, 8-12 μm), UV cameras or other direct or indirect image-producing sensor systems, such as radar or laser radar. Images from different sensor systems may also be combined by data fusion and be jointly displayed to the user.
In a system for indirect vision, the image sensors need not be positioned close to the user. The user may be located in any physical place. He is thus virtually in the place of the sensors although he is not located where the image sensors are positioned. To allow the user a good perception of the surrounding world, it should be captured and displayed in a field of vision that is as large as possible since this is the way in which we naturally experience the surrounding world. However, this cannot always be achieved; for instance, in a combat vehicle there is not much space for large screens. A way of solving this problem is to provide the user with a headworn display device which may consist of one or more miniaturised screens which are viewed via enlarging optics, or a device which projects/draws images directly on the user's retina.
In use of a headworn display device, an image can be displayed to a single eye, monocular display. When using two screens, the same image can be displayed to both eyes, biocular display, or two different images are displayed, one for each eye in what is referred to as binocular display. In binocular display, a stereoscopic effect can be achieved. By using additional screens adjacent to and outside (to the left and to the right of) screens straight in front of the eyes, a peripheral vision can also be achieved. The screens can preferably be indirectly fastened to the user's head by some kind of device similar to a spectacle frame or helmet.
The visual impression normally changes as the user's head moves. The image which, via a headworn screen, is displayed to a user is, however, usually not affected by the user's head moving relative to the surrounding world. The feeling of not being able to change the visual impression by movements is by most people using headworn screens experienced as frustrating after a while. The normal behaviour of scanning the surrounding world by turning the head and looking around does not work.
A solution to this is to detect the position and direction of the user's head by a head position sensor. The image displayed to the user by the headworn screen can then be adjusted so that the user experiences that he can look around himself.
By using indirect vision where the user carries a headworn display device and where the position and direction of the user's head are detected, the user in a combat vehicle may get a feeling of seeing through the walls of the vehicle, “See-Through-Armour”, in the following abbreviated STA.
Three techniques of providing an STA system will be presented below:
1. The STA system is based on an image sensor device which is placed on a gimbal, see FIG. 1, which is movable in several directions. The gimbal, which can be controlled from a head position sensor, can be oriented from the direction of a user's head. The image from the image sensor device is displayed to the user via a headworn display device.
2. The STA system is based on an image sensor device which captures the surrounding world by a plurality of image sensors where each image sensor captures a part of a large surrounding world, see FIG. 2. The user carrying a headworn display device will have image data displayed to himself, which is pointed out by a head position sensor.
Such a system is known from the article “Combat Vehicle Visualization System” by R. Belt, J. Hauge, J. Kelley, G. Knowles and R. Lewandowski, Sarnoff Corporation, Princeton, USA, published on the Internet at the address:
http://www.cis.upenn.edu/˜reich/paper11.htm.
This system is called “See Through Turret Visualization System” and is here abbreviated STTV. In the STTV, the images from a multicamera device are digitised by a system consisting of a number of electronic cards with different functions. The electronic cards contain, inter alia, image processors, digital signal processors and image memories. A master processor digitises the image information from the multi-camera device, selects image information of one or two cameras from the direction of a user's head and puts them together without noticeable joints in an image memory and then displays that part of the image memory which corresponds to the direction of the user's head. The STTV manages to superpose simple 2-dimensional, 2D, virtual image information, for instance a hairline cross or an arrow that indicates in which direction the user should turn his head. The direction of the user's head is detected in the STTV by a head position sensor which manages three degrees of freedom. The three degrees of freedom are often called yaw, pitch and roll by analogy with that applied in connection with aircraft. In an aircraft yaw is the head direction in which the longitudinal axis of the aircraft is directed, pitch the nose direction around a transverse axis through the wings (nose up/nose down) and roll the angle position around the longitudinal axis.
3. The STA system is based on an image sensor device which captures the surrounding world by means of a plurality of image sensors where each image sensor captures a part of a large surrounding world and where information from the image sensors is placed as dynamic textures in a 3D model in a computer graphics system. The user carrying a headworn display device will have image data displayed to himself from the 3D model according to output data of a head position sensor regarding the position and direction of the user's head.
Such a system is disclosed in Swedish Patent Application No. 0401603-6, “Device and Method for Presenting an Image of the Surrounding World”, with the same applicant and inventor as the present application.
In all these three systems, the direction of the user's head, and in some cases also the position of the head, controls which part of the surrounding world is to be displayed to the user.
With the user sitting on a chair or the like that cannot rotate, the user's surveillance of the surrounding world is limited owing to the limited mobility of his head. This could be attended to by means of a swivel chair, but in many cases, such as in a fighter aircraft, this is not practically possible. In addition, problems may arise by cables and other equipment getting entangled owing to the user's swivelling.